A$_1$-A$_2$ splitting in pure $^3$He in nematic aerogel

TL;DR

This study investigates the magnetic field dependence of superfluid transition temperature splitting in pure $^3$He within nematic aerogel, revealing nonlinear behavior and discrepancies with existing theories at various magnetic field strengths.

Contribution

It provides experimental evidence of nonlinear superfluid transition splitting in pure $^3$He in nematic aerogel across a wide magnetic field range, challenging current theoretical predictions.

Findings

Detected both upper and lower superfluid transition temperatures.

Observed nonlinear splitting at lower magnetic fields, contrary to theory.

Identified discrepancies between experimental results and theoretical models.

Abstract

Here, we present the results of vibrating wire experiments in pure $^3$He (without $^4$He coverage) in nematic aerogel. We investigated the dependence of splitting of the superfluid transition temperature of $^3$He in aerogel on magnetic field. In addition to our previous work, we used a wider range of magnetic fields (up to 31 kOe) and managed to detect both the "upper" and "lower" superfluid transition temperatures. The solid paramagnetic $^3$He layer on the aerogel strands activates the magnetic scattering channel. According to theory, it should result in linear splitting at high ($\ge20$ kOe) fields, while at lower fields the splitting is expected to be nonlinear. We were able to observe this nonlinearity, but we have a discrepancy with theoretical predictions regarding the range of fields where nonlinearity occurs. Possible reasons for this are discussed.